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Lenses are used in spectacles to treat some vision defects - Edexcel - GCSE Physics - Question 3 - 2015 - Paper 1
Question 3
Lenses are used in spectacles to treat some vision defects. The two main lens types are converging lenses and diverging lenses. (i) Diverging lenses always produce ... show full transcript
Worked Solution & Example Answer:Lenses are used in spectacles to treat some vision defects - Edexcel - GCSE Physics - Question 3 - 2015 - Paper 1
Step 1
Which row of the table describes the images produced by a converging lens?
Answer
The correct choice is B: 'either real or virtual' and 'either magnified or diminished'. A converging lens can produce both real and virtual images depending on the object distance. When the object is placed beyond the focal point, a real and magnified image is formed. When the object is placed within the focal point, a virtual and magnified image is produced.
Step 2
Describe how the power of a lens is related to its shape.
Answer
The Power of a Lens
The power of a lens, denoted as , is defined as the reciprocal of its focal length in meters: P = rac{1}{f}
where:
- is measured in diopters (D)
- is the focal length (in meters)
Relationship to Shape
The shape of a lens directly influences its focal length and, consequently, its power:
- Convex lenses (Converging lenses): These lenses are thicker at the center than at the edges. They have a positive focal length and can converge light rays to a point.
- Concave lenses (Diverging lenses): These lenses are thinner at the center and thicker at the edges. They have a negative focal length and cause light rays to diverge.
Conclusion
Thus, a lens's shape determines its ability to focus light, and this ability is quantified by the lens's power. A more curved lens (a shorter focal length) will have a higher power, allowing it to converge or diverge light more dramatically.